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diff --git a/Documentation/fb/uvesafb.txt b/Documentation/fb/uvesafb.txt new file mode 100644 index 000000000..aa924196c --- /dev/null +++ b/Documentation/fb/uvesafb.txt @@ -0,0 +1,184 @@ + +uvesafb - A Generic Driver for VBE2+ compliant video cards +========================================================== + +1. Requirements +--------------- + +uvesafb should work with any video card that has a Video BIOS compliant +with the VBE 2.0 standard. + +Unlike other drivers, uvesafb makes use of a userspace helper called +v86d. v86d is used to run the x86 Video BIOS code in a simulated and +controlled environment. This allows uvesafb to function on arches other +than x86. Check the v86d documentation for a list of currently supported +arches. + +v86d source code can be downloaded from the following website: + + https://github.com/mjanusz/v86d + +Please refer to the v86d documentation for detailed configuration and +installation instructions. + +Note that the v86d userspace helper has to be available at all times in +order for uvesafb to work properly. If you want to use uvesafb during +early boot, you will have to include v86d into an initramfs image, and +either compile it into the kernel or use it as an initrd. + +2. Caveats and limitations +-------------------------- + +uvesafb is a _generic_ driver which supports a wide variety of video +cards, but which is ultimately limited by the Video BIOS interface. +The most important limitations are: + +- Lack of any type of acceleration. +- A strict and limited set of supported video modes. Often the native + or most optimal resolution/refresh rate for your setup will not work + with uvesafb, simply because the Video BIOS doesn't support the + video mode you want to use. This can be especially painful with + widescreen panels, where native video modes don't have the 4:3 aspect + ratio, which is what most BIOS-es are limited to. +- Adjusting the refresh rate is only possible with a VBE 3.0 compliant + Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0 + compliant, while they simply ignore any refresh rate settings. + +3. Configuration +---------------- + +uvesafb can be compiled either as a module, or directly into the kernel. +In both cases it supports the same set of configuration options, which +are either given on the kernel command line or as module parameters, e.g.: + + video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel) + + # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module) + +Accepted options: + +ypan Enable display panning using the VESA protected mode + interface. The visible screen is just a window of the + video memory, console scrolling is done by changing the + start of the window. This option is available on x86 + only and is the default option on that architecture. + +ywrap Same as ypan, but assumes your gfx board can wrap-around + the video memory (i.e. starts reading from top if it + reaches the end of video memory). Faster than ypan. + Available on x86 only. + +redraw Scroll by redrawing the affected part of the screen, this + is the default on non-x86. + +(If you're using uvesafb as a module, the above three options are + used a parameter of the scroll option, e.g. scroll=ypan.) + +vgapal Use the standard VGA registers for palette changes. + +pmipal Use the protected mode interface for palette changes. + This is the default if the protected mode interface is + available. Available on x86 only. + +mtrr:n Setup memory type range registers for the framebuffer + where n: + 0 - disabled (equivalent to nomtrr) + 3 - write-combining (default) + + Values other than 0 and 3 will result in a warning and will be + treated just like 3. + +nomtrr Do not use memory type range registers. + +vremap:n + Remap 'n' MiB of video RAM. If 0 or not specified, remap memory + according to video mode. + +vtotal:n + If the video BIOS of your card incorrectly determines the total + amount of video RAM, use this option to override the BIOS (in MiB). + +<mode> The mode you want to set, in the standard modedb format. Refer to + modedb.txt for a detailed description. When uvesafb is compiled as + a module, the mode string should be provided as a value of the + 'mode_option' option. + +vbemode:x + Force the use of VBE mode x. The mode will only be set if it's + found in the VBE-provided list of supported modes. + NOTE: The mode number 'x' should be specified in VESA mode number + notation, not the Linux kernel one (eg. 257 instead of 769). + HINT: If you use this option because normal <mode> parameter does + not work for you and you use a X server, you'll probably want to + set the 'nocrtc' option to ensure that the video mode is properly + restored after console <-> X switches. + +nocrtc Do not use CRTC timings while setting the video mode. This option + has any effect only if the Video BIOS is VBE 3.0 compliant. Use it + if you have problems with modes set the standard way. Note that + using this option implies that any refresh rate adjustments will + be ignored and the refresh rate will stay at your BIOS default (60 Hz). + +noedid Do not try to fetch and use EDID-provided modes. + +noblank Disable hardware blanking. + +v86d:path + Set path to the v86d executable. This option is only available as + a module parameter, and not as a part of the video= string. If you + need to use it and have uvesafb built into the kernel, use + uvesafb.v86d="path". + +Additionally, the following parameters may be provided. They all override the +EDID-provided values and BIOS defaults. Refer to your monitor's specs to get +the correct values for maxhf, maxvf and maxclk for your hardware. + +maxhf:n Maximum horizontal frequency (in kHz). +maxvf:n Maximum vertical frequency (in Hz). +maxclk:n Maximum pixel clock (in MHz). + +4. The sysfs interface +---------------------- + +uvesafb provides several sysfs nodes for configurable parameters and +additional information. + +Driver attributes: + +/sys/bus/platform/drivers/uvesafb + - v86d (default: /sbin/v86d) + Path to the v86d executable. v86d is started by uvesafb + if an instance of the daemon isn't already running. + +Device attributes: + +/sys/bus/platform/drivers/uvesafb/uvesafb.0 + - nocrtc + Use the default refresh rate (60 Hz) if set to 1. + + - oem_product_name + - oem_product_rev + - oem_string + - oem_vendor + Information about the card and its maker. + + - vbe_modes + A list of video modes supported by the Video BIOS along with their + VBE mode numbers in hex. + + - vbe_version + A BCD value indicating the implemented VBE standard. + +5. Miscellaneous +---------------- + +Uvesafb will set a video mode with the default refresh rate and timings +from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo. + + +-- + Michal Januszewski <spock@gentoo.org> + Last updated: 2017-10-10 + + Documentation of the uvesafb options is loosely based on vesafb.txt. + |